The overall objective of the proposed research is to study pharmacological and environmental determinants of drug dependence by systematically investigating the control of behavior by scheduled injections of drugs. We will emphasize studies of the effects of chronically administered cocaine and other abused drugs, and studies of the suppression of drug-maintained behavior because of their recognized national priorities and potential practical significance. Studies involving chronic administration will determine: 1) how continuous exposure to cocaine, phencyclidine, and selected opiates affects behavior maintained by self-administered drugs and other consequences and 2) how such exposure alters the behavioral effects of drugs that may be used illicitly in conjunction with cocaine, phencyclidine or opiates. Studies involving the suppression of behavior will determine: 1) conditions under which response-produced noxious stimuli are effective in attenuating behavior maintained by self-administered cocaine and other drugs and 2) how acute treatment with selected anxiolytics and other drugs affect attenuated self-administration behavior. Behavior maintained by self-administration of drugs will be compared directly with behavior maintained under identical conditions by other consequences, such as presentation of food or termination of electric shock. The proposed research will provide needed quantitative information about the effects of chronic drug administration and suppressive noxious stimuli in relation to drug dependence.